Legionnaires’ Disease: Symptoms, Treatment, and How to Protect Yourself

An epidemiologist shares what you need to know about the bacterial lung infection, including how it’s spread and treated. 

This article originally appeared in NewYork-Presbyterian Health Matters.

By Camille Bautista-Fryer 

Bronx Voice 

August 31, 2025

NEW YORK - Legionnaires’ disease, a severe type of pneumonia caused by the Legionella pneumophila bacteria that grows in water, can cause flu-like symptoms such as coughing, muscle aches, and shortness of breath.

Reported cases of the serious lung infection have been increasing since the early 2000s, according to the Centers for Disease Control and Prevention, and a recent Legionnaires’ disease community cluster in New York City’s Central Harlem has included more than 80 cases to date, causing three deaths. As of August 8, no source has been confirmed for the outbreak, but the New York City Department of Health and Mental Hygiene has reported the likely source is a cooling tower in the affected area.

“The Legionella bacteria thrives in warmer water, between 68° and 113° F, and we do see a seasonal peak in the summer and late fall, partly related to air conditioning use because building water and ventilation systems may allow conditions for the bacteria to thrive,” says Dr. Matthew Simon, chief hospital epidemiologist at New York-Presbyterian Hospital/Weill Cornell Medical Center and the deputy medical director for infection prevention and control at NewYork-Presbyterian Hospital.

The bacteria can be hazardous when it grows in places such as water systems, cooling towers, and air conditioning and heating systems that are not properly maintained.

“The disease is not acquired through drinking water or transmitted from person-to-person; it’s acquired through inhalation of contaminated water,” says Dr. Simon. “Most healthy people who are exposed to the bacteria don’t get sick. While the condition isn’t spread from person to person, certain risk factors, such as age and chronic conditions, can put people at increased risk if they inhale contaminated water.”

Health Matters spoke with Dr. Simon to learn more about how Legionnaires’ disease is spread, and what to know about symptoms and treatment.

What is Legionnaires’ disease?

Legionnaires’ disease is a type of pneumonia or lung infection caused by the Legionella bacteria. In severe cases, it can lead to hospitalization, low oxygen, and in some instances, respiratory failure.

The bacteria can also cause a less severe, flu-like condition known as Pontiac fever, in which most people may not actually receive a confirmed diagnosis and can get better on their own.

How is Legionnaires’ disease spread?

Legionnaires’ disease is spread through the inhalation of mist or water droplets from contaminated water.

Sources can include whirlpools, jacuzzis, fountains, and cooling towers that are part of heating, ventilation, and air conditioning systems that are not properly cleaned or disinfected. If water in these HVAC systems becomes contaminated, the bacteria suspended in water droplets can be aerosolized off the tops of the affected buildings.

The disease is not contagious and can’t be spread from person-to-person contact.

What are symptoms of Legionnaires’ disease?

• Fever
• Cough
• Shortness of breath
• Muscle aches
• Diarrhea
• Confusion

Who is more at risk?

People with underlying conditions can be at higher risk of getting Legionnaires’ disease. 

The populations include those:

• Above 50
• Who smoke
• With comorbidities including chronic lung disease
• With weakened immune systems

How is Legionnaires’ disease diagnosed and treated?

Legionnaires’ disease can be diagnosed through a:

• Urine sample
• Respiratory culture looking at mucus from the lungs

A sputum (mucus) culture can be very important from a public health perspective because it allows for the health department to test and match it with an environmental sample to help determine the bacteria’s potential source.

Most cases of Legionnaires’ disease can be treated with antibiotics.  

When is it time to see a doctor?

If someone is experiencing high fevers, shortness of breath or and confusion, seek immediate care.